1. Field of the Invention
The present invention relates to a method of producing a core for magnetic head, and more particularly relates to a method of producing a narrow-track core for magnetic head by a laser-induced etching, which induces a chemical reaction by a laser light.
2. Description of the Related Art
There have been disclosed methods for forming a track portion of a core for magnetic head by a laser machining in Japanese patent Laid-open application Nos. 29,118/76, 212,617/82 and the like. Japanese patent Laid-open application No. 29,118/76 discloses a method, wherein a core having a width somewhat larger than the track width is formed, and both sides of the magnetic gap portion of the core is eliminated by a laser machining to define the track width. However, in this method, the machining proceeds through a mechanism, wherein a substance to be eliminated is heated, melted, evaporated and removed by a laser light, and therefore the machined surface has a processing strain due to the heat, accompanied with the formation of microcracks on the surface, and the resulting magnetic head has poor magnetic properties. Moreover, in this method, a melted substance to be eliminated is solidified and adhered to the machined surface and the vicinity thereof as illustrated in FIG. 10 to deteriorate the surface roughness of the machined surface and to cause ununiform thermal diffusion, and hence more than .+-.5 .mu.m of scattering is caused in the machined amount and the dimensional accuracy of the resulting track width is poor.
In order to obviate this drawback, Japanese patent Laid-open application No. 212,617/82 discloses a method, wherein unnecessary portion is first eliminated by a laser light having a high power density, and then a finishing machining is carried out by a laser light having a low power density in the above described method. This machining method can somewhat obviate such drawbacks that the melted substance to be eliminated is adhered to the machined surface and the vicinity thereof, and the dimensional accuracy of the resulting track width is poor due to the scattering of the machined amount caused by the ununiform thermal diffusion. However, in the use of a laser light having a low power density, the amount to be eliminated per one time of machining is as small as 5-10 .mu.m, and hence when a machined depth more than 5-10 .mu.m is required, the laser light must be repeatedly scanned, and a long machining time is required. Further, the elimination of a substance to be eliminated proceeds through a mechanism of melting and evaporation as proceeds in the above described method, and hence processing strain, microcracks and the like due to heat are formed on the machined surface, resulting in the deterioration of the properties of the resulting magnetic head. Moreover, in both of the above described methods, a core having already a predetermined core width is subjected to a track-forming machining, and therefore grooves formed on both sides of a track cannot be filled with glass in a commercial scale in order to protect the track after the track is formed. As the result, when the magnetic head is slid on a recording medium, such as magnetic tape, magnetic disc or the like, the track of the magnetic head is often broken, and the magnetic head is poor in reliability. In order to obviate these drawbacks, Japanese patent Laid-open application No. 260,408/86 discloses a method, wherein a so-called gapped bar, which has a large length and can produce a plural number of cores, is subjected to the above described laser machining to eliminate unnecessary portions and to form grooves or holes, whereby a plural number of tracks corresponding to the number of cores to be produced are formed and the eliminated portion is filled with glass to protect the track, and then the gapped bar is cut into a plural number of cores. However, in this case, when the gapped bar is subjected to the laser machining, heat is not uniformly diffused into the gapped bar as is uniformly diffused into a thin sheet-like core in the laser machining, and cracks are formed in the track portion. Accordingly, this method cannot be carried out in a commercial scale.
Japanese patent Laid-open application Nos. 82,780/80, 125,677/83 and 82,289/85 disclose methods, which belong to a technical field different from the machining for the production of magnetic head, and wherein a laser light is irradiated to ceramics or metal under a halogen gas or halide gas atmosphere to etch the ceramics or metal by a laser-induced etching. However, all of these three methods do not satisfy the requirements in order to obtain a high accuracy necessary for the production of magnetic head.
For example, Japanese patent Laid-open application No. 82,780/80 discloses the use of pulse laser. However, pulse laser has instantaneously a very high power, and therefore a substance to be eliminated is melted concurrently with the laser-induced etching of the substance, and processing strain, microcracks and the like due to the heat are formed in the remaining portion, resulting in the deterioration of the properties of the resulting magnetic head.
In the method disclosed in Japanese patent Laid-open application No. 125,677/83 also, a laser light having a fairly high power (0.5-1 KW) is used, and hence the above described drawbacks cannot be obviated.
Japanese patent Laid-open application No. 82,289/85 does not at all disclose the power of laser light, the gas pressure and the like, which are requirements necessary for obtaining a predetermined surface roughness. Therefore, in this method, machining of ferrite in a satisfactorily high accuracy is not able to be carried out.